title: Rapid changes in the electrical state of the 1999 Izmit earthquake rupture zone.
abstract: Crustal fluids exist near fault zones, but their relation to the processes that generate earthquakes, including slow-slip events, is unclear. Fault-zone fluids are characterized by low electrical resistivity. Here we investigate the time-dependent crustal resistivity in the rupture area of the 1999 Mw 7.6 Izmit earthquake using electromagnetic data acquired at four sites before and after the earthquake. Most estimates of apparent resistivity in the frequency range of 0.05 to 2.0 Hz show abrupt co-seismic decreases on the order of tens of per cent. Data acquired at two sites 1 month after the Izmit earthquake indicate that the resistivity had already returned to pre-seismic levels. We interpret such changes as the pressure-induced transition between isolated and interconnected fluids. Some data show pre-seismic changes and this suggests that the transition is associated with foreshocks and slow-slip events before large earthquakes.
authors.affiliation: Volcanic Fluid Research Center, Tokyo Institute of Technology, Tokyo, Japan. yhonkura@h05.itscom.net
authors.forename: Yoshimori
authors.initials: Y
authors.lastname: Honkura
authors.forename: Naoto
authors.initials: N
authors.lastname: Oshiman
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsushima
authors.forename: Serif
authors.initials: S
authors.lastname: Barış
authors.forename: Mustafa
authors.initials: M
authors.lastname: Kemal Tunçer
authors.forename: Sabri
authors.initials: S
authors.lastname: Bülent Tank
authors.forename: Cengiz
authors.initials: C
authors.lastname: Celik
authors.forename: Elif Tolak
authors.initials: ET
authors.lastname: Ciftçi